Amid widespread concern about its new privacy policies, Google is now facing criticism over an offer to give users Amazon gift certificates if they open their Web movements to the company in a program called Screenwise.

Google says the program launched "near the beginning of the year," but the company's low-key offer was disclosed Tuesday night on the blog Search Engine Land.

Google is asking users to add an extension to the Chrome browser that will share their Web-browsing activity with the company. In exchange, users will receive a US$5 Amazon gift when they sign up and additional $5 gift card values for every three months they continue to share. (Amazon is not a partner in the project.) Users must be over age 13, and minors will need parental consent to participate. The tracking extension can be turned off at any time, allowing participants to temporarily close their metaphorical shades on Google.

The company says the program will help it "improve Google products and services and make a better online experience for everyone."

Google declined to specify exactly how it would achieve those aims. A company spokesperson said, "Like many other web and media companies, we do panel research to help better serve our users by learning more about people's media use, on the web and elsewhere."

But David Jacobs, a consumer protection fellow at the Electronic Privacy Information Center, noted that the fine print of Google's announcement suggested the program might allow Google to track user behavior "at a higher level of detail" than it already does. The offer says Google will observe not just which websites users visit, but also "how [they] use them." Jacobs noted that the program could potentially capture behaviors like mouse-overs in addition to clicks.

Still, privacy advocates saw some positives to the program, mainly that it is purely opt-in. Both Jacobs and Justin Brookman, director of the Consumer Privacy Project at the Center for Democracy and Technology welcomed that approach.

Brookman saw it as a positive sign about what Google will do with its planned new ability to combine data from a single user's interactions with multiple products. Privacy advocates worry the company could build detailed user profiles. With the Chrome tracking program, Google is looking for equally detailed information from a single user.

"They're really asking to lift up the hood," Brookman said. "It's a good sign that they're saying it has to be on an opt-in basis."